We are continuing our work on the immunobiology of the Ia bearing cells in the skin. We will further examine their kinetics of repopulation as a model for repopulation of macrophages in general. This will be examined directly as it has important impacts on our studies on bone marrow chimeras and the role of H-2 in antigen presenting cells. We will further examine the cellular responses to minor histocompatability antigens and the role of H-2 in their presentation. These will be carried out both using biochemical and immunological approaches as well as genetic efforts.